idr: fix unexpected ID-removal when idr_remove(unallocated_id)

If unallocated_id = (ANY * idr_max(idp->layers) + existing_id) is passed
to idr_remove().  The existing_id will be removed unexpectedly.

The following test shows this unexpected id-removal:

  static void test4(void)
  {
        int id;
        DEFINE_IDR(test_idr);

        printk(KERN_INFO "Start test4\n");
        id = idr_alloc(&test_idr, (void *)1, 42, 43, GFP_KERNEL);
        BUG_ON(id != 42);
        idr_remove(&test_idr, 42 + IDR_SIZE);
        TEST_BUG_ON(idr_find(&test_idr, 42) != (void *)1);
        idr_destroy(&test_idr);
        printk(KERN_INFO "End of test4\n");
  }

ida_remove() shares the similar problem.

It happens only when the caller tries to free an unallocated ID which is
the caller's fault.  It is not a bug.  But it is better to add the
proper check and complain rather than removing an existing_id silently.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/idr.c

@@ -562,6 +562,11 @@ void idr_remove(struct idr *idp, int id)
 	if (id < 0)
 		return;
 
+	if (id > idr_max(idp->layers)) {
+		idr_remove_warning(id);
+		return;
+	}
+
 	sub_remove(idp, (idp->layers - 1) * IDR_BITS, id);
 	if (idp->top && idp->top->count == 1 && (idp->layers > 1) &&
 	    idp->top->ary[0]) {
@@ -1025,6 +1030,9 @@ void ida_remove(struct ida *ida, int id)
 	int n;
 	struct ida_bitmap *bitmap;
 
+	if (idr_id > idr_max(ida->idr.layers))
+		goto err;
+
 	/* clear full bits while looking up the leaf idr_layer */
 	while ((shift > 0) && p) {
 		n = (idr_id >> shift) & IDR_MASK;